Engine Vibration

Tiny
AAW501
  • MEMBER
  • 2000 FORD WINDSTAR
  • 3.8L
  • V6
  • FWD
  • AUTOMATIC
  • 100,000 MILES
The engine vibrates badly. We have replaced the torque converter because the Ford mechanic said it was bad and the balancing shaft looks good, but it still shakes. What could be causing the engine to shake so badly? Could it be a problem with the harmonic balancer?
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Monday, May 16th, 2016 AT 4:10 PM

13 Replies

Tiny
CARADIODOC
  • EXPERT
Before you go looking for more obscure things, look at the simple / common stuff. How long since the spark plugs were replaced? You may have nothing more than a misfire due to worn plugs.
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Monday, May 16th, 2016 AT 6:29 PM
Tiny
AAW501
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We had all that checked. They said all of that was good. There was a internal problem with the engine.
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Monday, May 16th, 2016 AT 6:40 PM
Tiny
CARADIODOC
  • EXPERT
If someone looked at this already, what was their diagnosis? The balance shaft is not likely to cause a problem unless someone had it out and reinstalled it incorrectly.

Do not overlook a collapsed engine mount that is letting the two metal parts of the brackets hit each other. That will transmit normal engine vibration into the body.
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Monday, May 16th, 2016 AT 7:02 PM
Tiny
AAW501
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They said the torque converter and the balancing shaft were the problem, but we do not think either one of those are the problem. We were going to check the engine mounts, but the dealership told us it was a problem inside the engine. That's why the only other thing we could think of was the harmonic balancer?
What do you think?
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Monday, May 16th, 2016 AT 7:40 PM
Tiny
CARADIODOC
  • EXPERT
I cannot find a picture of your harmonic balancer to know which style you have. Most have an outer ring that is glued to the center hub. Many years ago those lasted the life of the vehicle, but now, for some reason, it is somewhat common for that jelly to let go and the ring can spin on the hub. The place where that usually causes a problem is when there is a timing mark on that ring. That puts it in the wrong place.

Some engines are "externally balanced", meaning there are two counterweights they could not cast as part of the crankshaft. Instead, you will find a small weight welded to the torque converter or flex plate, and weight added to the hub of the harmonic balancer. The only way the heavy spot on the harmonic balancer could shift is if the keyway was broken apart or the key sheared off to allow the hub to rotate on the snout of the crankshaft. That is not common, but eventually the balancer would slip so badly that the serpentine belt would stop driving the generator and power steering pump. You would also feel the slop when you tried to wiggle the balancer.

Some harmonic balancers, mostly on import engines, have the pulley for the serpentine belt cast as part of the outer ring. On those, if that ring slips, eventually it will burn the bonding material away and fall off.

The clue to a mechanical imbalance problem is the vibration will change a lot with changes in engine speed. At idle you might not notice any problem, but at a certain higher speed, (the harmonic), the vibration will get real bad. At a still higher speed it may be less noticeable. Think of the pendulum on a grandfather's clock. There is only one speed at which it takes very little energy to keep it swinging. You have to exert a lot more force to make it swing faster or slower than its normal speed. A crankshaft bends in the middle due to the forces put on it by the connecting rods. There is a happy speed that is its natural speed, just like the clock pendulum, at which very little energy is needed to keep that occurring. However, the actual energy being input by the connecting rods stays constant, so in effect, way more energy than what is needed is being put into it. (As a point of interest, big block Chevy engines that are run real fast, as in around 7,500 rpm, often break into three pieces on the race track due to that bending along with the use of special lightweight harmonic balancers and flywheels). If your engine's happy speed where the vibrations occur is 700 rpm, every multiple of that is a harmonic, meaning the vibration will be worst at 1,400, 2,100, 2,800, etc. Rpm. The harmonic balancer is weighted and designed to dampen those vibrations, and they do a real good job. Even if they did not, you won't break a crankshaft because the forces being put into it are nowhere near what is encountered in a race engine.
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Monday, May 16th, 2016 AT 8:38 PM
Tiny
AAW501
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Okay. Thanks for explanation. Since the harmonic balancer might not be the problem and the torque converter is new, what else do think could be the problem?
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Monday, May 16th, 2016 AT 9:34 PM
Tiny
CARADIODOC
  • EXPERT
You need a professional's opinion. If this only occurs at idle or low speeds, a stuck-open EGR valve will cause rough running. Many engines do not use EGR valves so you need someone who can look at it and feel the vibration.

In the early 1970's Chrysler had some muscle car engines that used externally-balanced crankshafts. They were famous for excellent parts interchangeability between years and models, and this included the ability to install the wrong harmonic balancer and / or flywheel for the crankshaft being used. That resulted in an irritating vibration that some people just lived with. For your problem, it would be obvious if the problem developed right after a part was replaced. Since that is not the case, a broken part would cause other symptoms besides just a vibration, so you have to look for things that does not apply to. For example, torque converters lock up at highway speed for better fuel mileage. If that lock-up clutch was slipping, you'd have a noticeable chatter for one or two seconds when that occurred; typically around 35 - 40 mph. Tapping on the brake pedal will make that chatter occur again.

A cracked hub on a harmonic balancer will cause a knocking noise that will quiet a little if the engine is run without the serpentine belt.

As I recall, your balance shaft is run by a pair of gears so that is not likely to get out-of-time on its own. You mentioned that was checked, but it takes more than just looking at the shaft. The timing marks must be checked. If it were possible for something to jump time, the equivalent of one tooth off on a balance shaft is enough to cause a noticeable vibration.

You can also try disabling one cylinder at a time to verify it is not a misfire causing this. If you find one where there's no change in how the engine is running when you unplug an injector, ignition coil, or spark plug wire, look closer at compression and camshaft lobes for that cylinder.
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Monday, May 16th, 2016 AT 9:55 PM
Tiny
AAW501
  • MEMBER
Okay. Thank you very much! You really helped out a lot. We are going to sleep on it and I might talk to you in morning about it if we come up with another idea.
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Monday, May 16th, 2016 AT 10:18 PM
Tiny
CARADIODOC
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I had a major house fire two years ago so I do not have internet access at home. I drive into town, usually every other day, to see how you are doing. Do not panic if you do not hear from me right away.
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Monday, May 16th, 2016 AT 10:20 PM
Tiny
AAW501
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Okay. Thanks again.
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Monday, May 16th, 2016 AT 10:43 PM
Tiny
RENEE
  • ADMIN
Awesome in-depth and thorough answers CARADIODOC! Keep it up! We really appreciate you.

Renee
Admin
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Tuesday, May 17th, 2016 AT 3:47 PM
Tiny
POTATO2
  • MEMBER
I found my 3.8 harmonic balancer pulley moved
this dont throw codes. The engine just had bad vibration. You can see the position of the weighted balancer to position of key slot from old balancer on right to new on left. The engine is running very smooth no shaking at all.
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Friday, September 15th, 2017 AT 2:09 PM
Tiny
CARADIODOC
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Thanks for your addition. Your dandy photo shows that this is yet a third design. Most of the trouble comes from those that use the outer cast iron ring as the pulley. That is bonded to the hub, and that gel can let go, then the weighted pulley can rotate on the hub. Older balancers used a non-weighted one-piece cast iron balancer with a stamped steel pulley bolted to it. It looks like yours is a one-piece design with an offset weight pressed onto the hub. Just another way of doing the same thing.
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Friday, September 15th, 2017 AT 7:15 PM

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